Problem mixing image with shaders
Assuming that you don't want to apply the shader to the actual face of the texture, all you need to do is plug the alpha of the image texture into the mix shader socket. This should make the faintly discoloured box disappear, as it will only apply the ColorRamp to anything that isn't the face.

Shader setup:



Result:



If this doesn't work, then check:


The face has an alpha of 1, and everything else has an alpha of 0.
The shaders on the "Mix Shader" node are in the correct order.